1. Field of the Invention
The present invention relates to front opening unified pods, or FOUPs, and in particular to a laterally floating latch hub assembly provided in the FOUP door or port door to increase the tolerance of the latch assembly for mating with the driven latch keys and to minimize FOUP error at port.
2. Description of Related Art
A SMIF (Standardized Mechanical Interface) system proposed by the Hewlett-Packard Company is disclosed is U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes into semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest.
FOUPs (Front Opening Unified Ports) are in general comprised of a vertically oriented FOUP door which mates with a FOUP shell to provide a sealed, ultraclean interior environment in which wafers may be stored and transferred. The wafers are supported in either a cassette mounted to the interior of the shell, or to shelves mounted to the interior of the shell.
In order to transfer wafers between a FOUP and a process tool within a wafer fab, a FOUP is typically loaded either manually or automatedly onto a load port on a front of the tool so that the pod door lies adjacent the port door of the process tool. The port door includes a pair of rotatable latch keys, which keys are capable of mating within respective slots in the FOUP door to accomplish two objectives. Once the doors are positioned adjacent each other and the keys are located in the slots, rotation of the keys actuate a latch assembly within the FOUP door to decouple the FOUP door from the FOUP. Details relating to such a latch assembly within the FOUP door are disclosed for example in U.S. Pat. No. 4,995,430, entitled xe2x80x9cSealable Transportable Container Having Improved Latch Mechanismxe2x80x9d, to Bonora et al., which patent is owned by the assignee of the present application. Second, rotation of the latch keys within the slots couples the FOUP door to the port door, so the doors may thereafter be moved together out of and away from the port to allow wafer transfer between the FOUP and the process tool. Upon completion of wafer processing, the port door returns the FOUP door to the FOUP. At this point, rotation of the latch keys in the opposite direction decouples the port and FOUP doors and again latches the FOUP door to the FOUP.
It is necessary to precisely and repeatably control the position of the front surface of the FOUP door on the load port to ensure a clean mating of the FOUP door to the port door. In order to establish the desired position, conventional load port assembly systems include kinematic pins on a horizontal support surface, which pins mate within slots on the bottom of the FOUP to support the FOUP in a fixed and repeatable position. However, a problem with conventional front opening load port assemblies is that, while the horizontal surface of the FOUP seated on the kinematic pins is precisely positioned, the actual position of the front surface of the FOUP door is not precisely controlled and may vary as much as approximately 25 mils to either side. Sources of this variance include warping, improper construction and tolerances of the FOUP, improper seating of the FOUP door in the FOUP, and tolerances in the location of the kinematic pins.
This variance between the expected and actual relative positions of the FOUP and port doors is significant because the maximum tolerance for the port door latch keys to fit properly in the FOUL door slots is approximately xc2x15 mils. A greater variance than that may result in contact between the latch keys and the walls defining the FOUP slots, thereby generating particulates. Where the variance is significant, it can also cause a xe2x80x9cFOUP error at portxe2x80x9d, where the load port controller recognizes an error and stops the process. The load port would then sit idle until a technician can attend to the problem. As there can be several hundred load ports in a wafer fab, each susceptible to FOUP error at port due to misalignment of the latch keys with the FOUP slots, this problem can significantly impact production throughput and has become a significant concern to wafer manufacturers. Prior art attempts to solve this problem include beveling both the latch keys and slots, but this solution has proven only partially effective in alleviating the problem.
It is therefore an advantage of the present invention to provide a positionally tolerant system whereby a latch key can properly engage within a FOUP slot even upon an initial misalignment.
It is a further advantage of the present invention to provide a laterally floating latch hub assembly which maybe easily incorporated into existing latch assembly designs.
It is a further advantage of the present invention to provide a laterally floating latch hub assembly which can effectively transmit torque from the latch keys to the latch assembly.
It is a further advantage of the present invention to provide a laterally floating latch hub assembly which can be incorporated into a FOUP door without changing the outer configuration or dimensions of the FOUP door or FOUP.
These and other advantages are provided by the present invention which in preferred embodiments relates to a laterally floating latch hub assembly. In preferred embodiments, the laterally floating latch hub assembly includes a latch key receptor translatably mounted within a rotatable latch actuation cam. Upon advancing a FOUP to a load port assembly, the latch keys within the port door are received within the latch key receptor, which is capable of translating laterally to ensure a proper fit of the latch key within the receptor. Once received within the receptor, torque from the latch keys is transmitted to the latch actuation cam via the latch key receptor. It is additionally or alternatively contemplated that the latch keys in the port door be translatably mounted to a driven hub within the port door so that the latch keys themselves may shift laterally to ensure a proper fit of the keys within the latch assembly in the FOUP.